Automatic volume control



Oct. 23, 1934. W L L 1,978,182-

AIJTOMA'I'IC VOLKIIME CONTROL Filed July 2, 1932 K p L IL; 7 w- INVENTOR Patented Oct. 23, 1934 UNITED7STATES 1,978,182 AUTOMATIC VOLUME CONTROL Karl Wilhelm, Berlin-Charlottenburg, Germany,

assignor to Siemens & Halske Aktiengesellschaft, Siemensstadt, near Berlin, Germany, a corporation of Germany Application July 2, 1932, Serial No. 620,559

In Germany September 5, 1931 8 Claims. (01. 250-) The present invention relates to circuit arrangements for automatic amplitude regulation in signal transmitter systems.

Because of fading phenomena which are ob- 1,1,! servedin the reception of long distance wireless transmitter systems or stations, and which are liable to seriously disturb reproduction or signal reading while all other conditions may be perfect, recourse has been had to automatic amplii 0. tude regulators which usually operate by keeping at a constant value the carrier wave potential across the demodulator. In practicing such a regulation method it would seem most advantageous from a practical viewpoint to alter the radio frequency amplification by varying the biasing Igrid potential of the radio frequency amplifier tubes, and to use as the control voltage the platedirect current potential of the demodulator, this being. a function of the radio frequency po- Z tential to be demodulated.

1 fluctuations of volume level. Hence, the necesa sity toamplify the controFpotenti-alderived from therdemodulator before the same is fed to the amplifier to be regulated. It isknown in theprior art to use for this amplification of the control 11 0 potential :2, distinct tubewhich, since very slow potential variations are dealt with, is most, suitably of the direct current amplifier type. However, the use of such a separate tube especially where relatively small receiver stations are concerned, such as broadcast receivers forwhich the cost is of decisive importance, means an inadmissible extra expense.

Now, according to the present invention this. difliculty is obviated by that the amplification of 2 0 the direct current control potential is efiected in one or more amplifiers provided, for the ampli fication of the incoming signal. Fundamentally speaking, any desired amplifier, say, a radio frequency amplifier, and intermediate frequency amplifier, or elsean audio frequency-amplifier,

orany desired combination thereof, or else a rectifying amplifier'could be used therefor. Also the gain variation serving for amplitude regulation may be effected at any suitable point. As

: a general rule, however, iit is of advantage that the point at which the amplitude regulation of the signal currents occursshould be locatedxahead of, or bEIOWgthB signal currentamplifier or ame plifiers insuring the directcur-rent amplification i of the control potential. Using this fundamental rule in connection with receiver apparatus comprising a plurality of radio frequency amplificati'on stages, this means that in one or more of the initial radio frequency stages thereoccurs the amplitude regulation of the signal current, and in one or more of the subsequent radio frequency stages the direct current amplification of the control potential.

The drawing shows an embodiment of the in-' vention as incorporated in a three circuit receiver usable for broadcast reception and comprising a two-stage radio frequency amplification. The incoming radio frequency potential is fed by way of the first tuning circuit Sl,inoluded in the aerial circuit, to the first radio frequency tube V1 which, for instance, may be of the screen grid type. r The plate circuit of this tube V1, in well known manner, is coupled, by way of a stopper circuit S2, with the grid circuit of a second radio frequency tube V2 which likewise may be of the screen grid type. The plate circuit of this tube is in coupling relationship, by way of a. third. tuned circuit S3, with the grid circuit, say, of a rectifier tube G connected audion-fashion, and the plate circuit thereof contains the primary winding of a low frequency (audio frequency) transformer T. Across the output terminals A of the latter the audio frequency potential resulting from the demodulation may be collected, and be fed on to other amplifier stages in a Way well known in the prior art.

In orderto make the over-all gain of the receiver apparatus a function of the incoming radio frequency amplitude, the grid circuit of the radio frequency tube V1 is so connected with the plate circuit of the rectifier tube Gthat with increasing radio frequency amplitudes, owing to the ensuing change in the mean plate potential of the rectifier, the grid biasing potential of the radio frequency is shifted towards the negative end to a corresponding degree. In this scheme, according to the invention, the second radio frequency amplifier tube V2 serves for the amplification of the direct current potential which is to be fed into the first radio frequency amplifier tube V1 as a variable grid biasing potential. With this end in View the end of the grid leak R2 of the tube V2 turned away fromthe grid is not connected with alfixed potential, but is connected with a definite point of the plate circuit of the rectifier tube G containing the resistances R4 and :R6,the tapping point being here chosen mostsuitably in such a' way that the grid biasi'ng potential of the tube V2 in unexcited state, 1

i. e., in the absence of reception, is negative in reference to the filament.

Similarly, also, the grid leak resistance R1 of the first radio frequency tube V1 is not connected with a fixed potential, but is coupled byway of a resistance R5 electrically with the plate circuit of the second radio frequency tube V2 so that the plate potential of the second radio frequency tube forms at the same time the grid bias of the first radio frequency tube.

In actual operation, as the radio frequency volume level rises, the grid potential of the second radio frequency tube V2, as a result of decreasing plate current in the rectifier tube G, is shifted towards the positive end so that the potential acting at the plate of the tube V2 becomes lower, and thus the grid biasing potential of the first radio frequency tube V1 becomes shifted towards the negative end. The size of such a shift in the first radio frequency tube is appreciably greater than in the second tube since the latter acts as a direct current amplifier for the control direct current potential.

As long as no radio frequency energy reaches the rectifier the grid potential of the first radio frequency tube V1 is shifted towards the positive end. There exists a danger of the grid current then initiated causing such a damping in the incoming radio frequency energy that the radio frequency energy reaching the rectifier will be insufficient for the actuation of the regulator. In the grid circuit of the second radio frequency tube V2 a similar action might arise in .the presence of radio frequency amplitudes growing beyond a certain measure. In order to meet this danger, therefore, the grids of the two tubes are blocked in a way as shown in the diagram of connections.

In order that the building of the circuit scheme may be as much simplified as feasible in spite of the inter-dependence of the grid and plate circuits due to the direct current amplification, and so that the filaments may be beatable from a single source, an advisable plan is to employ indirectly heated tubes, at least to use this type for the two radio frequency tubes. The filament or heating circuits H of the three tubes may then be fed either in series'or in parallel,

. say, from the direct current or alternating current network, it being, of course, necessary in this connection to be able to adjust the plate and screengrid potentialsin a definite way. For this purpose a common or joint voltage divider resistance (potentiometer) R7 is most suitably used in a way as shown which is connected with the direct current potential N furnished directly from the direct current network or resulting from rectification of the alternating current furnished from the alternating current network.

The invention is by no means confined to the use in connection with receiver circuits for radio transmission systems. Indeed, it will be found useful for all kinds of signal transmission systems wherein automatic amplitude regulation is accomplished by the aid of a control direct current potential. It is moreover immaterial in so far as the applicability or usefulness of the basic idea of this invention is concerned whether the said control direct current is obtained by the rectification of alternating current potential or whether it consists of a directly obtained direct current potential.

While I have indicated and describedone arrangement for carrying my invention into effect,

it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described, but that many modifications may be made without departing from the scope of my invention as set forth in the appended claims.

What is claimed is:

1. In combination with a radio receiver including at least two cascaded high frequency amplifiers and a following rectifier, means for impressing the direct current component of the rectifier output on an input electrode of the amplifier immediately preceding it, and a direct current connection between the output circuit of the last amplifier and a gain control electrode of the first of said cascaded amplifiers.

2. In combination, a high frequency amplifier whose gain is to be automatically regulated, a second amplifier for amplifying the high frequency output of the first amplifier, a rectifier connected to the second amplifier output, means for impressing the direct current component of the rectifier output on the second amplifier whereby the latter amplifies the said component, and means for applying the amplified component to a gain control electrode of the first amplifier for said gain regulation.

3. In an automatic volume control system for a radio receiver, the latter including a pair of radio amplifiers and a detector all in cascade, a direct current connection between the detector anode circuit and the signal grid circuit of the next preceding amplifier, and a second direct current connection between the anode circuit of the last named amplifier and the signal grid circuit of the first of said pair of amplifiers.

4. In combination in a radio receiver including at least two cascaded radio frequency amplifiers, the first of said amplifiers including a resonant input circuit, a resonant network coupling the anode circuit of the first amplifier with the input electrodes of the second amplifier, a detector stage including a tube having its input electrodes coupled to the anode circuit of said second amplifier, a resonant network connected to the detector input electrodes, a resistor in the anode circuit of said detector, a direct current connection between the control grid of the second amplifier and said resistor, a second resistor in the anode circuit of said second amplifier, and a direct current connection between the control grid of said first amplifier and said second resistor. 5. In combination in a radio receiver including at least two cascaded radio frequency amplifiers, the first of said amplifiers including a resonant input circuit, a resonant network coupling the anode circuit of the first amplifier with the input electrodes of the second amplifier, a detector stage including a tube having its input electrodes coupled to the anode circuit of said second amplifier, a resonant network connected to the detector input electrodes, a resistor in the anode circuit of said detector, a direct current connection between the control grid of the second amplifier and said resistor, a second resistor in the anode circuit of said second amplifier, and a direct current connection between the control grid of said first amplifier and said second resistor, said first direct current connection being adjustably connected to said first resistor. 6. In combination in a radio receiver including at least two. cascaded radio frequency amplifiers, the first of said amplifiers including a resonant input circuit, a resonant network coupling the anode circuit of the first amplifier with the input electrodes of the secondamplifier, a detector stage including a tube having its input electrodes coupled to the anode circuit of said second amplifier, a resonant network connected to the detector input electrodes, a resistor in the anode circuit of said detector, a direct current connection between the control grid of the second amplifier and said resistor, a second resistor in the anode circuit of said second amplifier, a direct current connection between the control grid of said first amplifier and said second resistor, a common source of energizing potential for the electrodes of said amplifiers and detector, a resistor connected across said common source, and connections from said resistor to the electrodes of said amplifiers and detector.

7. ,In combination in a radio receiver including at least two cascaded radio frequency amplifiers, the first of said amplifiers including a resonant input circuit, a resonant network coupling the anode circuit of the first amplifier with the input electrodes of the second amplifier, a detector stage including a tube having its input electrodes coupled to the anode circuit of said second amplifier, a resonant network connected to the detector input electrodes, a resistor in the anode circuit of said detector, a direct current connection between the control grid of the second amplifier and said resistor, a second resistor in the anode circuit of said second amplifier, a direct current connection between the control grid of said first amplifier and said second resistor, a common source of energizing potential for the electrodes of said amplifiers and detector, a resistor connected across said common source, and connections from said resistor to the electrodes of said amplifiers and detector, said second and third resistors being connected in series between the anode of the second amplifier and the negative side of said common potential source.

8. In combination in a radio receiver including at least two cascaded radio frequency amplifiers, the first of said amplifiers including a resonant input circuit, a resonant network coupling the anode circuit of the first amplifier with the input electrodes of the second amplifier, a rectifier stage including a tube having its input electrodes coupled to the anode circuit of said second amplifier, a resonant network connected to the rectifier input electrodes, a resistor in the space current path of said rectifier, a direct current connection between the control grid of the second amplifier and said resistor, a second resistor in the space current path of said second amplifier, and a direct current connection between the control grid of said first amplifier and said second resistor.

, KARL WILHELM. 

